The present invention relates generally to process control systems and, more specifically, to an intelligent linking device and method for interfacing smart field devices that use a standard communication protocol to a process control system which may not use that communication protocol.
Modem process control systems are typically microprocessor-based distributed control systems (DCSs). A traditional DCS configuration includes one or more user interface devices, such as workstations, connected by a databus (e.g., Ethernet) to one or more controllers. The controllers are generally physically close to a controlled process and are connected to numerous electronic monitoring devices and field devices such as electronic sensors, transmitters, current-to-pressure transducers, valve positioners, etc. that are located throughout the process.
In a traditional DCS, control tasks are distributed by providing a control algorithm within each of the controllers. The controllers independently execute the control algorithms to control the field devices coupled to the controllers. This decentralization of control tasks provides greater overall system flexibility. For example, if a user desires to add a new process or part of a process to the DCS, the user can add an additional controller (having an appropriate control algorithm) connected to appropriate sensors, actuators, etc. Alternatively, if the user desires to modify an existing process, new control parameters or control algorithms may, for example, be downloaded from a user interface to an appropriate controller via the databus.
To provide for improved modularity and inter-manufacturer compatibility, process controls manufacturers have more recently moved toward even further decentralization of control within a process. These more recent approaches are based on xe2x80x9csmartxe2x80x9d field devices that communicate using an open protocol such as the HART(copyright), PROFIBUS(copyright), WORLDFIP(copyright), Device-Net(copyright), CAN, and FIELDBUS(copyright) protocols. These smart field devices are essentially microprocessor-based devices such as sensors, actuators, etc. that, in some cases, such as with Fieldbus devices, also perform control loop functions traditionally executed by a DCS controller. Because some smart field devices provide control capability and communicate using an open protocol, field devices from a variety of manufacturers can communicate with one another on a common digital databus and can interoperate to execute a control loop without the intervention of a traditional DCS controller.
The Fieldbus communication protocol is one particularly popular open communication protocol that is used by some smart field devices. As is generally known, Fieldbus provides both synchronous (i.e., scheduled) communications and asynchronous (i.e., token ring type) communications on a protocol bus, these communications being performed according to a bus schedule created by the system designer. The schedule may define when each device or software component within a device can communicate on the bus, when different components should execute, when asynchronous communications take place, etc. In general, the scheduled/synchronous communications are used for signals related to actual process control activities while the asynchronous communications are used to convey secondary information, for example, to and from a user or to implement other activities not directly necessary for process control.
In operation, the control process may require information to be exchanged between the field devices. For example, the synchronous communications on the protocol bus may be scheduled so that one of the field devices provides information (e.g., function block parameters) to another one of the smart field devices on the protocol bus. Similarly, the asynchronous communications on the protocol bus may be used to convey other information such as configuration information between the smart field devices and the user interface.
Prior art process control systems do not allow a seamless integration of smart field devices because they do not enable the linking of field device information, such as function block information resident in one or more of the field devices, with function block information resident in the controller. As a result, function block information associated with a given control loop must reside entirely within the controller or entirely within the field devices on a given protocol bus.
Additionally, with current linking devices and methods, troubleshooting communication problems and configuration errors associated with the field devices on the protocol bus is very difficult because current devices do not automatically monitor and/or analyze the communications on the protocol bus. As a result, users at the system level cannot easily identify a problem, for example, with a particular one of the field devices and are typically only informed by the system via the user interface that the overall process is not operating properly.
The invention provides an intelligent linking device that enables the seamless integration of smart field devices that are communicatively coupled via a nonproprietary protocol bus with a process control system having one or more controllers that do not necessarily communicate using the non-proprietary protocol. Generally speaking, the liking device functions as a communication gateway or bridge that seamlessly conveys information resident in the one or more smart field devices to a controller and seamlessly conveys information resident in a controller to one or more smart field devices. More particularly, function block information resident in the field devices is linked with function block information in a controller so that control loops can be more flexibly configured to include combinations of field device function blocks and controller resident function blocks, thereby eliminating the above-noted constraint of prior art systems.
Additionally, the intelligent linking device monitors and analyzes the communications on the field device protocol bus to enable the troubleshooting of communication problems, configuration errors, etc. from a user terminal at the system level. Specifically, the linking device may compare actual synchronous and asynchronous communications on the protocol bus to a link active schedule, which defines scheduled times at which particular field devices should be communicating on the bus, to identify possible communication problems with particular field devices that would otherwise be extremely difficult for a system user to identify using conventional troubleshooting techniques.
A method in accordance with one aspect of the invention enables interfacing between a plurality of field devices communicatively coupled together via a communication network that uses a standard communication protocol to a controller and a user interface. The method uses a linking device coupled to the controller and the field devices and includes the steps of monitoring substantially all communications on the communication network using the linking device, selectively processing at least some of the monitored communications in the linking device to produce first field device information that is associated with at least one of the field devices, and sending the first field device information to the controller.
The method may further include the steps of generating second field device information in the controller and sending the second field device information to at least one of the field devices. The first and second information may include function block information.
The step of selectively processing the monitored communications may include the steps of producing diagnostic information associated with the communications on the communication network, producing information associated with the linking and timing of the communications on the communication network, producing communication statistics associated with the communications on the communication network, and/or producing identification information associated with one of the field devices. The method may further include the steps of comparing the identification information to commissioning information stored in a memory of the linking device, determining a discrepancy between the commissioning information and the identification information based on the comparison, and notifying a user of the discrepancy.
In accordance with yet another aspect of the invention, a linking device for interfacing with a plurality of field devices having function blocks communicatively coupled via a communication network that uses a standard communication protocol and a controller, includes a communication stack communicatively coupled to the communication network that uses the communication protocol to monitor substantially all communications on the communication network. The linking device may further include a connection manager that uses the communication stack to coordinate communications on the communication network, a function block data manager that selectively processes at least some of the monitored communications to produce function block information associated with at least one of the field devices, and a database manager that sends the function block information to the controller.
The linking device may also include a diagnostic manager that selectively processes at least some of the monitored communications to produce diagnostic information associated with the communications on the communication network. The linking device may further include a live list manager that stores a live list identifying the devices attached to the communication network, and an auto-sense manager that uses the live list to selectively process the monitored communications to produce identification information associated with at least one of the field devices on the communication network.